The present invention relates to a windscreen wiper for an automobile, and more particularly, it relates to an improvement on a wiper driving apparatus of the type that both functions to automatically stop the wiper blade at a fixed position and to operate the wiper blade intermittently are provided.
Various types of wiper driving apparatuses for an automobile or the like are known in the art. One of the types, on the one hand, determines an automatic fixed stop position of the wiper blade by means of a metal plate mounted on one side of a reduction gear train which is driven by a wiper motor and a contact lever in operative association with the metal lever and mounted on a housing of the gear train, and on the other hand, in cooperation with the above determining function, operates intermittently the wiper blade by means of an external relay unit which is externally mounted relative to the combined arrangement of the metal plate and the contact lever. Another of the types, on the one hand, determines an automatic fixed stop position by means of a cam formed by providing a difference in relative positions in a reduction gear train and a limit switch, microswitch or the like which is actuated by the cam, and on the other hand, in cooperation with the above determining function, operates intermittently a wiper blade by means of some external relay units.
Conventional wiper driving apparatuses with the above functions have been found, however, not satisfactory in that since the external relay unit and the wiper motor are separately mounted on an automobile and therefore connection is required therebetween with the help of wiring leads, it is ineffective in assembling them on the automobile frame. More in particular, for the former type wiper driving apparatus, connectors and lead wires are required for the relay unit so that the number of components increase. And for the latter type wiper driving apparatus, connectors and lead wires for some external relay units are required so that the same problem as above, that is, increase of the number of components, arises.
Referring now to FIG. 1 wherein a typical prior art control circuit for the wiper driving apparatus is shown, reference number 1 denotes diagrammatically shown switches for actuating a wiper blade, reference number 2 denotes a wiper motor, and reference number 3 denotes a relay unit. In operation, for example, either a particular switch for a low speed command or a particular switch for a high speed command in the wiper switch 1 is turned on, the motor 2 is driven into rotation with the terminal A or B grounded through the wiper switch 1. Thus, a wiper blade coupled for association with the motor 2 through a speed reduction mechanism, crank linkage, or the like, is reciprocally swung.
During high or low speed operation of the wiper blade, upon turning OFF the wiper switch 1, the current having passed through the terminal A or B to ground by way of the particular switch for a low speed or high speed command is terminated. In this case, if a cam switch S1 operatively coupled to the wiper motor 2 is in contact with a contact P at the time instant when the wiper switch 1 is turned OFF, the wiper motor 2 still continues to rotate. This is because that a current is supplied to the wiper motor through a path from a plus power source terminal, wiper motor 2, terminal A, wiper switch 1, terminal b of the relay unit 3, NC contact of a switch S2, terminal C, and to P1 terminal of the switch S1. Alternatively, if the cam switch S1 operatively coupled to the wiper motor 2 is in contact with a contact P2 at the time instant when the wiper switch 1 is turned OFF, the wiper motor 2 stops in this case. This is because that a current supply to the wiper motor 2 is completely terminated and moreover an electromagnetic brake is generated by a closed circuit having a path from one end of the wiper motor 2, contact P2 of the switch S1, NC contact of the switch S2, wiper switch 1, and to the other end of the wiper motor 2.
The intermittent operation is effected by turning on a particular switch for intermittent operation of the wiper switch. In this case, a terminal a of the relay unit 3 is grounded by way of the particular switch for intermittent operation so that a transistor TR1 is turned on to thereby render a relay coil 4 conductive. Then, a movable contact of the relay switch S2 moves to an NO contact.
As a result, the terminal A of the wiper motor 2 for a low speed operation is grounded through a path from wiper switch 1, terminal b of the switch S2, contact NO, terminal a, wiper switch 1, and to ground. Accordingly, the wiper motor 2 is driven at a low speed. The intermittent operation is attained in the following manner.
While the cam switch S1 is in contact with the contact P1, a transistor TR2 becomes turning on so that the transistor TR1 is cut off setting in turn the movable contact of the relay switch S2 at the contact NC. With the relay switch S2 connecting to the contact NC, the wiper motor 2 continues to rotate with a current passing through the terminal C and through the terminal P1 of the cam switch S1 until the wiper blade comes to an automatic fixed stop position. During the rotation, a capacitor C1 is charged in a short time through a small resistor R0.
When the wiper blade comes to the automatic fixed position, the cam switch S1 detects this and the cam switch S2 is set at the contact P2. As a result, the contact P2 and hence the terminal c of the relay unit 3 is supplied with a positive voltage from the power source. Although a path for supplying a sufficient base current for turning on the transistor TR1 is interrupted, a discharge current from the capacitor C1 keeps the transistor TR2 being saturated for a predetermined time, whereby the wiper motor stops for the predetermined time. And after completion of the discharge, the transistor TR2 is turned off to again initiate the actuation of the wiper blade by making the transistor TR1 conductive and hence by moving the movable contact of the switch 2 to the contact NO. The above operation is repeated to achieve an intermittent operation as desired.
It is noted that in a conventional wiper driving apparatus of the type described above, the wiper motor 2 including the cam switch S1 for attaining the automatic fixed stop position and the relay unit 3 including the relay switch S2 are arranged separately from each other so that the structure becomes complicated and the assembly on an automobile is very ineffective.